    # Call an API with given options.
    #
    # @return [Array<(Object, Integer, Hash)>] an array of 3 elements:
    #   the data deserialized from response body (could be nil), response status code and response headers.
    def call_api(http_method, path, opts = {})
      request = build_request(http_method, path, opts)
      response = request.run

      if @config.debugging
        @config.logger.debug "HTTP response body ~BEGIN~\n#{response.body}\n~END~\n"
      end

      unless response.success?
        if response.timed_out?
          fail ApiError.new('Connection timed out')
        elsif response.code == 0
          # Errors from libcurl will be made visible here
          fail ApiError.new(:code => 0,
                            :message => response.return_message)
        else
          fail ApiError.new(:code => response.code,
                            :response_headers => response.headers,
                            :response_body => response.body),
               response.status_message
        end
      end

      if opts[:return_type]
        data = deserialize(response, opts[:return_type])
      else
        data = nil
      end
      return data, response.code, response.headers
    end

    # Builds the HTTP request
    #
    # @param [String] http_method HTTP method/verb (e.g. POST)
    # @param [String] path URL path (e.g. /account/new)
    # @option opts [Hash] :header_params Header parameters
    # @option opts [Hash] :query_params Query parameters
    # @option opts [Hash] :form_params Query parameters
    # @option opts [Object] :body HTTP body (JSON/XML)
    # @return [Typhoeus::Request] A Typhoeus Request
    def build_request(http_method, path, opts = {})
      url = build_request_url(path)
      http_method = http_method.to_sym.downcase

      header_params = @default_headers.merge(opts[:header_params] || {})
      query_params = opts[:query_params] || {}
      form_params = opts[:form_params] || {}

      {{#hasAuthMethods}}
      update_params_for_auth! header_params, query_params, opts[:auth_names]
      {{/hasAuthMethods}}

      # set ssl_verifyhosts option based on @config.verify_ssl_host (true/false)
      _verify_ssl_host = @config.verify_ssl_host ? 2 : 0

      req_opts = {
        :method => http_method,
        :headers => header_params,
        :params => query_params,
        :params_encoding => @config.params_encoding,
        :timeout => @config.timeout,
        :ssl_verifypeer => @config.verify_ssl,
        :ssl_verifyhost => _verify_ssl_host,
        :sslcert => @config.cert_file,
        :sslkey => @config.key_file,
        :verbose => @config.debugging
      }

      # set custom cert, if provided
      req_opts[:cainfo] = @config.ssl_ca_cert if @config.ssl_ca_cert

      if [:post, :patch, :put, :delete].include?(http_method)
        req_body = build_request_body(header_params, form_params, opts[:body])
        req_opts.update :body => req_body
        if @config.debugging
          @config.logger.debug "HTTP request body param ~BEGIN~\n#{req_body}\n~END~\n"
        end
      end

      request = Typhoeus::Request.new(url, req_opts)
      download_file(request) if opts[:return_type] == 'File'
      request
    end

    # Builds the HTTP request body
    #
    # @param [Hash] header_params Header parameters
    # @param [Hash] form_params Query parameters
    # @param [Object] body HTTP body (JSON/XML)
    # @return [String] HTTP body data in the form of string
    def build_request_body(header_params, form_params, body)
      # http form
      if header_params['Content-Type'] == 'application/x-www-form-urlencoded' ||
          header_params['Content-Type'] == 'multipart/form-data'
        data = {}
        form_params.each do |key, value|
          case value
          when ::File, ::Array, nil
            # let typhoeus handle File, Array and nil parameters
            data[key] = value
          else
            data[key] = value.to_s
          end
        end
      elsif body
        data = body.is_a?(String) ? body : body.to_json
      else
        data = nil
      end
      data
    end
